A system including a first circuit, a second circuit, an amplifier, and a summer. The first circuit is configured to (i) select a first portion of a signal, and (ii) generate a first compensation for asymmetry in the first portion of the signal using a first function, where the first function is a modulus function. The second circuit is configured to (i) select a second portion of the signal, and (ii) generate a second compensation for asymmetry in the second portion of the signal using a second function, where the second function is different than the first function. The amplifier amplifies the signal and provides an amplified output. The summer is configured to add (i) the first compensation, (ii) the second compensation, and (iii) the amplified output, where (i) the first circuit, (ii) the second circuit, and (iii) the amplifier are connected in parallel to the summer.
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8. A method comprising:
selecting (i) a first portion of a signal, and (ii) a second portion of the signal;
generating a first compensation for asymmetry in the first portion of the signal using a first function, wherein the first function is a modulus function;
generating a second compensation for asymmetry in the second portion of the signal using a second function, wherein the second function is different than the first function;
amplifying the signal;
receiving, in parallel, (i) the first compensation, (ii) the second compensation, and (iii) the amplified signal; and
adding, in parallel, (i) the first compensation, (ii) the second compensation, and (iii) the amplified signal.
1. A system comprising:
a first circuit configured to (i) select a first portion of a signal, and (ii) generate a first compensation for asymmetry in the first portion of the signal using a first function, wherein the first function is a modulus function;
a second circuit configured to (i) select a second portion of the signal, and (ii) generate a second compensation for asymmetry in the second portion of the signal using a second function, wherein the second function is different than the first function;
an amplifier configured to amplify the signal and to provide an amplified output; and
a summer configured to add (i) the first compensation, (ii) the second compensation, and (iii) the amplified output,
wherein (i) the first circuit, (ii) the second circuit, and (iii) the amplifier are connected in parallel to the summer.
2. The system of
the first function is of a form γ=βx+α|x|; and
the second function is (i) a linear function of a form γ=αx, (ii) an exponential function of a form γ=αex, or (iii) a polynomial function of a form
3. The system of
the first circuit is configured to (i) select the first portion of the signal based on a first offset, (ii) amplify the first portion of the signal according to the first function, and (iii) scale the amplified first portion based on a first factor to generate the first compensation; and
the second circuit configured to (i) select the second portion of the signal based on a second offset, (ii) amplify the second portion according to the second function, and (iii) scale the amplified second portion based on a second factor to generate the second compensation.
4. The system of
5. The system of
6. The system of
7. The system of
9. The method of
the first function is of a form γ=βx+α|x|; and
the second function is (i) a linear function of a form γ=αx, (ii) an exponential function of a form γ=αex, or (iii) a polynomial function of a form
10. The method of
selecting (i) the first portion of the signal based on a first offset, and (ii) the second portion of the signal based on a second offset;
amplifying (i) the first portion of the signal according to the first function, and (ii) the second portion according to the second function; and
scaling (i) the amplified first portion based on a first factor to generate the first compensation, and (ii) the amplified second portion based on a second factor to generate the second compensation.
11. The method of
12. The method of
13. The method of
generating a piecewise approximation of a region of the signal based on (i) the first compensation and (ii) the second compensation,
wherein the region includes at least the first portion and the second portion of the signal.
14. The method of
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This is a continuation of U.S. patent application Ser. No. 13/453,584, filed on Apr. 23, 2012, which is a continuation of U.S. patent application Ser. No. 11/835,936 (now U.S. Pat. No. 8,164,845), filed on Aug. 8, 2007. The entire disclosures of the above applications are incorporated herein by reference.
Hard disk drive transducing heads, including magneto-resistive (MR) heads, can provide an asymmetric output for a variety of reasons well known to ordinarily skilled artisans. Such reasons include, but are not limited to age, temperature, thermal asperity, current changes, and the like. When an output is asymmetric, the output waveform, desirably substantially sinusoidal, can have a positive portion of the waveform that is more substantial than a negative portion thereof (or vice versa).
Various asymmetry correction approaches have been tried over the years, including providing second order and/or third order corrections, or exponential corrections, or corrections which include a modulus function. One deficiency in these approaches is their validity extends only within a relatively limited range of unsaturated states of the head. Outside of that limited range, the results tend to diverge, and are less desirable.
In view of this and other deficiencies, it would be desirable to have an asymmetry correction system which provides a valuable approximation to an appropriate asymmetry correction over a wider range.
The invention now will be described in detail with reference to one or more embodiments and also with reference to the following drawings, in which:
To achieve the foregoing and other objects, in accordance with one embodiment of the invention, a piece-wise linear approximation to an asymmetry correction curve is provided, in which the number of pieces is selectable, and the type of correction (e.g. linear, exponential, higher-order, modulus) provided for each of the pieces also is selectable.
Objects and advantages of the present invention will become apparent from the following detailed description. For convenience, the following description refers to MR heads, but the invention is applicable to any apparatus in which asymmetry correction is necessary.
Referring to
In
The value x also goes into a correction block 404 which includes an offset block 406, as noted previously, and a modulus amplifier 408. The output of that modulus amplifier 408, y1, is scaled by a scaler 410 with a factor α, and the output i2, also passes through the summer 412 to yield the result y.
As many breakpoints, or as few breakpoints as desired (a number N are shown in
For each of the individual blocks providing offsets d1, d2, . . . , dn, y=f(x,d). The following relationships pertain:
One advantage of the arrangement of
One result of the embodiment of
As can be appreciated from the foregoing, the amount of complexity of the overall circuit is a linear function of the number of breakpoints desired. For example, providing four breakpoints would result in roughly four times the complexity of an implementation with a single breakpoint.
The value of α will define the amount of compression or expansion of a waveform in order to provide a substantially sinusoidal waveform, compensating for asymmetry. Changing d and α changes the slopes and breakpoints, and provides a piece-wise linear approximation of a fairly precise magneto-resistive asymmetry.
As can be appreciated from the foregoing, according to the invention, using circuitry that is easily implementable and provides piece-wise linear functions, any desired asymmetry compensation of any order can be approximated within a desired range.
While the foregoing description has been provided with respect to one or more embodiments, various modifications within the scope and spirit of the invention will be apparent to those of working skill in the relevant technological field. Thus, the invention is to be limited by the scope of the following claims.
A non-transitory computer program product containing program code for performing a method for compensating for asymmetry in waveform of an input signal is also provided. The method includes outputting a first compensation as a first function and outputting a second compensation as a second function. The first and second compensations together provide a piecewise approximation to at least one region of a saturation curve.
Singh, Mahendra, Annadore, Sriharsha
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